This invention relates to magnetic flowmeters and in particular to a family of flowmeters having the novel characteristic of utilizing the same coil driving power and producing substantially the same voltage output for a given average flow velocity over a wide range of sizes, from less than two inches in diameter to over twenty inches in diameter.
In an electromagnetic flowmeter, electromagnet coils arranged around a flow tube are energized by a driver circuit to produce a magnetic field across the flow tube. The magnetic field generates a voltage in a fluid flowing through the tube. The voltage, which is proportional to flow rate, is sensed by a pair of electrodes in contact with the fluid, and is amplified by a different amplifier to produce a flow-dependent signal which is amplified by a signal processing system to produce an output signal proportional to flow rate. Generally, the coils are provided with a core of ferromagnetic material, either in the form of an external yoke or in the form of the body of the meter tube when the coils are placed inside the tube. The driver circuit and the signal processing system are generally separate components which must, nonetheless, be separately designed for different sizes of meters. For example, the driver circuit may consume about twenty-five watts of power for a three inch diameter meter, and require about one hundred-fifty watts for a thirty inch meter.